1. Field of the Invention
The present invention relates to a video-signal-processing device and a video-signal-transfer method that can be used for producing a display image of a video signal generated based on the national television system committee (NTSC) system, for example. The present invention allows assigning a single frame of a color-difference signal to each of a plurality of frames of a brightness signal so that the center value on a time base generated by the single frame of the color-difference signal becomes closest to the center value on a time base generated by the plurality of frames of the brightness signal corresponding to the color-difference signal. Subsequently, it becomes possible to effectively avoid an unnatural display image of an edge and efficiently process a video signal with a high frame frequency by using a simple configuration.
2. Description of the Related Art
It has been known that the quality of a moving picture becomes high by increasing a frame frequency. However, where the frame frequency is increased without consideration, the information amount of a video signal transferred increases in proportion to the increased frame frequency. Therefore, there have been proposed methods for preventing the video-signal-information amount from being increased, so as to produce a moving picture with a high frame frequency.
For example, Japanese Unexamined Patent Application Publication No. 2003-348620 discloses a method for transmitting a brightness signal and a color-difference signal, where the frame frequency of the color-difference signal is decreased, so as to be lower than that of the brightness signal, increasing the decreased frame frequency of the color-difference signal by performing interpolation calculation on the reception side, and producing a display image of a video signal including the brightness signal and the color-difference signal. However, where the above-described interpolation calculation is performed for increasing the frame frequency of the color-difference signal, the configuration for achieving the interpolation calculation becomes complicated.
Accordingly, one and the same frame of the color-difference signal may be externally transmitted via a memory so that the frame frequency of the color-difference signal increases. The above-described method allows producing a high-quality object image as long as the object image is presented, as a still picture. However, where the object image is presented, as a moving picture, the edge of the object becomes significantly unnatural.
In each of FIGS. 11 and 12, an object image is shown by using a broken line and black circles, where the broken line indicates brightness signals and the black circles indicate color-difference signals. In FIG. 11, the frame frequency of the color-difference signal is the same as that of the brightness signal, and the object image is moved at a predetermined speed with time. Where an audience tracks the movement of the object image with his eyes, the object image is formed at a predetermined position on his retinas, as shown in FIG. 12. Subsequently, the audience can enjoy the moving object image without problems. Namely, in the case of FIGS. 11 and 12, the edge of the moving object image can be shown without problems.
However, where the color-difference signal is transferred for every three frames and displayed by repetitively transmitting one and the same frame, an object image presented on a display screen is moved intermittently for every three frames due to the above-described color-difference signal, as shown in FIG. 13 in comparison with FIG. 11. Subsequently, the object image generated by the color-difference signal is moved with a wave-like motion for every three frames with reference to a position recognized due to the brightness signal on the retinas of the audience tracking the movement of an object image generated by the brightness signal, as shown in FIG. 14 in comparison with FIG. 12.
In that case, therefore, the edge of the object image generated by the brightness signal becomes different from that of the object image generated by the color-difference signal, whereby both the edges blur. Further, the edge generated by the brightness signal and that generated by the color-difference signal are displaced from each other. If the frame frequency is low, the above-described blur and displacement are visually recognized, as a flicker.